Diesel engines having the aforementioned flow control actuators including variable geometry turbochargers (VGT) and variable nozzle turbochargers (VNT) (hereinafter collectively referred to as VGT/VNT), exhaust gas recirculation valves (EGR) and intake throttle valves (ITV) are well known. With respect to VGT/VNT and EGR, since both interact with exhaust gas flow there is characteristically significant and substantial interaction and cross-effects (control-coupling) therebetween. It is generally understood that such interaction requires control accounting if they are to be used simultaneously. Conventionally, however, calibration addresses such interaction by the use of ad-hoc set-point and control logic characterized by open-loop boost control operation when the EGR valve is open. Generally, then, the EGR valve is closed when torque is demanded by the driver (e.g. high speed/load operation) and opened once torque demand goes down (e.g. low speed/load operation).
Similarly EGR and ITV both effect control upon the engine mass airflow (MAF) in to the intake manifold. Sensed MAF is often used to control both EGR and ITV positioning; however, since both EGR and ITV interact with MAF there is characteristically significant and substantial interaction and cross-effects therebetween. Conventionally, and similar to the aforementioned EGR and VGT/VNT cross-effects, the EGR and ITV interaction is addressed through independent control of the individual actuators wherein one is used to the substantial exclusion of the other.
While such turbocharged diesel engine control and calibration for EGR and VGT/VNT may provide, on balance, satisfactory results (e.g. low NOx and soot emissions) in substantially steady-state or quiescent operation, certain transient operation may result in undesirable levels of emissions, with respect to both temporal and drive-cycle averaged results. This is due to the transient interaction between the aforementioned charge-handling system components (EGR, VNT/VGT and ITV) and to the generally conservative EGR and turbo-boost calibration scheduling.
Therefore, there is a continuing need in the art for controlling emissions in internal combustion engines. A need exists to improve internal combustion engine controls which may be compromised by cross-effects between charge-handling components. These cross-effects can be substantial and unless addressed will lead to degraded responses, instability and unacceptable performance and emissions. Additional improvements to emissions are particularly desirable during transient operating conditions.